Method for segregating metals and minerals from one another by leaching

ABSTRACT

A method for extracting metals from minerals is provided that involves the leaching of metals with a leaching agent comprised of a biomass of microorganisms having a chemo-organotrophic type of exchange which are grown in a nutrient medium. The microorganisms having chemo-organotropic type of exchange are selected from natural materials and may include acetic bacteria, pseudomonades, and sulfuric bacteria. The leaching is carried out with the consumption of biomass not less than 3×10 −3  kg per 1 kg of mineral raw material. A water solution of higher carbohydrate polymers is used as a nutrient medium and a mineral additive may be added thereto. Phosphate of ammonia, ammonium chloride, a mixture of phosphate of ammonia and ammonium chloride, or sodium chloride is used as the mineral additive. Vegetative residues, sawdust, cane, sedge, and household wastes are used as the higher carbohydrate polymers.

BACKGROUND OF THE PRESENT INVENTION

[0001] The present invention relates to a method for segregating metals and minerals from one another and, in particular, to a method for segregating metals such as silver and gold from minerals in connection with mining and other industries.

[0002] One conventional method for extracting metals from minerals is described in Design And Operation Of A Commercial Bacterial Oxidation Plant At Fairview/Tub Asweden P.C., Marais H. Y., Haines A. K. Marshalltown, 1988 (12 pages) and involves leaching by autotrophic acidophilic microorganisms Thiobacillus ferrooxidans with subsequent cyanidation of the leaching products. However, this method has the disadvantages of yielding only a low degree of extraction and of having a toxicity associated with the process.

[0003] Another conventional method for extractions of metals from minerals is described in Mining Journal, 1990, Vol. 314, No. 8068, pages 335-337 and involves leaching by the microorganisms Thiobacillus ferrooxidans in reactive tubs and subsequent sorption cyanidation in the presence of activated charcoal. A disadvantage of this method is its low degree of extraction of metals due to the presence in the ore of carbonaceous minerals comprised of rocks having predominantly a non-silicate composition. In connection with the oxidization of sulfide minerals by carbothionic bacteria, if the minerals contain more than 1% carbonates, sulfuric acid must be introduced into the medium. This need to introduce sulfuric acid sharply reduces the profitability of the bioprocess. Moreover, toxic cyanide dissolvent is used in the process.

[0004] A further conventional method, described in Russian Federation Patent No. 2059005, published Apr. 27, 1996, is a method for extracting metals from ores and involves leaching with a leaching agent of aqueous extract of vegetative residues. The disadvantages of this method include its low degree of metal extraction and the relatively lengthy duration of the process due to the fact that some of the autochthonous microflora (microorganisms living in the minerals involved in the process) which develop because of the presence of the aqueous extract of vegetative residues do not participate in the metal extraction process and the number of those microorganisms which do participate in the metal extraction process is insufficient to sustain an industrial scale commercially viable metal extraction output. Moreover, the development time of autochthonous microflora is lengthy and necessitates the creation of conditions favorable to such development.

SUMMARY OF THE INVENTION

[0005] The present invention provides a method for segregating metals and minerals from one another and, more specifically, the present invention provides a method for extracting metals from minerals which provides an improved rate of extraction and can be performed on raw material which is difficult to process.

[0006] The method of the present invention for extracting metals from minerals involves the leaching of metals with a leaching agent comprised of a biomass of microorganisms having a chemo-organotrophic type of exchange which are grown in a nutrient medium. The microorganisms having chemo-organotropic type of exchange are selected from natural materials.

[0007] In accordance with the method of the present invention, the leaching is carried out with the consumption of biomass not less than 3×10⁻³ kg on 1 kg of mineral raw material. Also, in accordance with the method of the present invention, acetic bacteria, pseudomonades, and sulfuric bacteria are used as microorganisms having chemo-organotropic type of exchange.

[0008] Additionally, in accordance with the method of the present invention, a water solution of higher carbohydrate polymers is used as a nutrient medium. In further connection with the nutrient medium, a mineral additive is added thereto. Phosphate of ammonia, ammonium chloride, a mixture of phosphate of ammonia and ammonium chloride, or sodium chloride is used as the mineral additive.

[0009] Vegetative residues, sawdust, cane, sedge, and household wastes are used as the higher carbohydrate polymers.

[0010] The method of the present invention is characterized in that a biomass of microorganisms having chemo-organotropic type of exchange grown in a nutrient medium is used as a leaching agent. The microorganisms having chemo-organotropic type of exchange form with the metals stable water-soluble chelate compounds in a broad pH range of the medium (ranging from acidic to alkaline) and the microorganisms having chemo-organotropic type of exchange, due to symbiotic links, provide combined effects on metals to be extracted from the minerals—that is, each of the microorganisms—symbiotes benefit one another and the degree of extraction of metals from the solution is increased.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0011] The following example illustrates an application of the method of the present invention.

EXAMPLE 1

[0012] The wastes of pyrite enrichment were subjected to metal leaching in accordance with the method of the present invention.

[0013] The percent chemical composition of the wastes of pyrite enrichment was:

[0014] Au—0.0003105; Fe—22.3; P—0.02; Cr—0.08; Cu—0.1; Zn—0.3; Ag—0.00212; Ca—0.92; Si—18.79; Al—2.12; Na—0.4; Ti—0.13; K—0.55; As—0.1

[0015] The percent mineral composition of the wastes of pyrite enrichment was:

[0016] Pyrite—55%, quartz—27%, and the balance comprised of feldspar, sericite chlorite, and calcite.

[0017] The wastes of pyrite enrichment were leached by the heap method in which lixiviating or leaching solution was filtered through motionless crushed mining mass in a column.

[0018] The leaching plant comprised a polyvinyl chloride plastic column having a false bottom covered by a fiberglass fabric layer so as to preclude the downward discharge of ore. A drain tap was provided in the bottom portion of the column.

[0019] The leaching conditions were as follows: Ore specimen 1 kg Crushing −2 + 0.5 mm Temperature 22-23° C. Aeration natural Liquid to solid ratio 0.3 Watering daily Duration 2 months Physical parameters of the ore: Specific gravity 4.8 ton/m³ Volume weight 1.58 ton/m³ Porosity 0.24 Moisture capacity 24% Factor of filtration 1.69 m/day

[0020] The leached wastes of pyrite enrichment were disposed in a layered manner in the column. Each layer was wetted by a biomass of microorganisms having chemo-organotropic type of exchange. Selected microorganisms were withdrawn from the natural material and grown in a nutrient medium of higher carbonate polymers. A biomass of microorganisms was obtained thereby. The leaching agent was comprised of an aqueous medium (pH 7.2) with the following percent composition:

[0021] Dry vegetative residues: 2.5%;

[0022] Ammonium phosphate double substituted: 0.03%; and

[0023] A biomass of microorganisms having chemo-organotropic type of exchange: 1% relative to the volume of the lixiviating solution.

[0024] The consumption of the biomass was 4×10⁻³ kg on 1 kg of wastes of pyrite enrichment.

[0025] The mining mass was watered daily at the rate of 40 liters per 1m² for a period of 60 days. The values of pH, chemical, and microbiological analyses were systematically monitored in the drain solutions. Following the completion of the tests, the contents of the metals were determined and the material composition of each layer was analyzed.

[0026] Table 1 shows the results of the extraction of metals from the solution. TABLE 1 Extraction, % Layer Au Ag Zn Cu 1 70 96 63 48 2 71 99 60 45 3 74 97 67 47

[0027] Table 2 shows the comparative data on the change of material composition of the wastes of pyrite enrichment after the heap leaching of the metals. TABLE 2 Components Initial ore, % Rest of the ore after leaching, % Pyrite 55 I layer - not present II layer - 2.5 III layer - 3 Chalcopyrite, cubanite 1.5 not present Blende, galena 0.8 not present Barite 8 4.5 0 Quartz 27 I layer - 76 II layer - 85 III layer - 76 Muscovite, hydromica 2 I layer - 9 II layer - 5 III layer - 8 Feldspars 3 I layer - 10.5 II layer - 7 III layer - 8 Clayey minerals <0.5 1 Sulfates <0.5 3

[0028] The transfer of metals into solution was caused by these reactions:

[0029] complexation with metastable products of pyrite oxidation by sulfite-thiosulfate ions [Au(SO₃)₂ ³⁻, Au(S₂O₃)₂ ³⁻];

[0030] the formation of chelate compounds of metals with microbial metabolites; and

[0031] the formation of chelate compounds with humus acids of the leaching agent.

[0032] It is noted that, in addition to the live bacterial cells and their metabolites, non-living organisms were present such as, for example, organic components (amino acids) entering the medium in connection with the process of the destruction of the living organisms and these non-living organisms are potential complexing agents.

EXAMPLE 2

[0033] Quartz-tinstone-sulfide ores were leached by a vat leaching method.

[0034] The percent chemical composition comprised:

[0035] Ag—0.0078; Zn—2.0; Cd—0.1; Ti—1.0; Fe—10.37

[0036] As—0.8; Si—28.1; Mg—0.36; Ca—0.09; Na—0.03

[0037] K—2.4; Sn—0.3; In—0.05

[0038] The percent mineral composition comprised:

[0039] Pyrite—30%, pyrrhotine—2%, arsenopyrite—1%, tinstone—1%,

[0040] blende—4%, stannite—2%, sulphosalts of silver, tin, lead—2%, and rock forming minerals in the form of quartz, tourmaline, alephibol, chlorite, and muscovite.

[0041] The initial conditions for the leaching process were as follows:

[0042] A charge of 18 kg of ore having particles of 0.15 mm size was loaded through a hatch into a tub having a working capacity of 180 liters. Leaching agent comprised of a biomass of microorganisms having chemo-organotropic type of exchange was loaded into the tub in the amount of 162 liters. The solid to liquid ratio was 1:10. The process was carried out at T=23° C. under aerobic conditions, the aerobic conditions being created by the agitation of the pulp without additional aeration. A mechanical agitator operating at 150 revolutions per minute assisted in the agitation. The duration of the agitation of the pulp was 10 hours a day. Any solution which settled during the night was purged and a new proportional charge of a leaching agent was introduced into the pulp in a manner to maintain the same initial ratio. The productive solutions were analyzed. The duration of the leaching in the periodic agitation mode was 22 days.

[0043] Table 3 shows the results of the extraction of metals into solution. TABLE 3 Extraction % Ag Zn Sn Cd In As 85 50 50 70 70 70

[0044] An analysis of the mineral composition of the remainder non-leachate after the completion of the leaching showed an absence of blende (zinc mineral) in the initial sample. Residues of arsenopyrite (arsenic mineral) were found in the form of eroded grains resulting from the bacterial leaching. Stannite (tin metal) has a corroded appearance and essential differences were revealed in a comparison with the stannite in the initial ore charge:

[0045] Percent composition of stannite in the initial ore charge:

[0046] Cu—30%, Fe—13%, Sn—27.6%, S—29.8%, As—0.2%

[0047] Percent composition of stannite after bioleaching:

[0048] Cu—27%, Fe—15%, Sn—23.5%, S—27%, As—0.05%

[0049] This data indicate the leaching of tin. Argentiferous minerals were not found in the remainder non-leachate.

EXAMPLE 3

[0050] Ore of a no longer used copper mine was subjected to underground leaching.

[0051] The percent chemical composition of the ore was:

[0052] SiO₂—22.62%, Al₂O₃—0.43%, Fe—34.4%, Ca—0.1%, Cu—3%, Zn—1%, K—0.2%, Na—0.2%

[0053] The percent mineral composition of the ore was:

[0054] Pyrite—60%, minerals of copper: chalcopyrite—8-10%, covellite, cubanite, cuprite, bornite, malachite, native copper—approximately 1%, quartz—24%

[0055] The upper zone of the deposit was comprised of oxidized ores; the middle zone of the deposit was comprised of ores of secondary enrichment; and the lower zone of the deposit was comprised of sulfides containing chalcopyrite and pyrite.

[0056] An explosion crushed 400,000 tons of ore and 200,000 tons of rocks. The explosion exposed split ore along the face with terraces having a height of 6.1 m and a width of between 4.6 m to 55 m. The average size of the pieces was 230 mm.

[0057] A biomass of microorganisms having chemo-organotropic type of exchange was used as a leaching agent grown in a nutrient medium, which was a water solution of higher carbonate polymers with the mineral additive sodium chloride. The leaching agent was fed at a ratio of 3×10⁻³ kg per 1 kg of ore by pumps via two pipelines having a diameter of 150 mm and a throughput of 3.785 m³/minute, with the leaching agent being flowed to the top of the slope whereupon it was fed through a distributive pipeline with a diameter of 51 mm and having spray nozzles every 12.2 m arranged to irrigate the surface of the terraces. Each nozzle watered 18.3 m³ and the total watered area comprised 75,000 m². The lixiviating solution had a pH of 7.2. The interval between waterings was no greater than 3 months. During the course of the collective watering periods, leaching of the copper was effected by the microorganisms due to the products of their metabolism, the components of the water solution of the medium (the leaching agent) and the oxygen in the ambient air. Iron and zinc additionally passed into the solution. The solutions comprising copper migrated downwardly due to gravity through the openings in and between the mined material to collect at the bottom of the excavation site and the solutions were then pumped therefrom via an operating well to the surface. The copper component in the thus produced solutions was 1-1.5 g/l.

[0058] The thus produced solutions were fed into a storage container, thereafter fed via pipeline at a feeding rate of approximately 4 m³/minute to another vessel, and subsequently disposed in a grout chamber for extraction of the copper from the solutions.

[0059] Table 4 herebelow shows the results of the extraction of metals from the solutions. TABLE 4 Extraction, % Cu Zn Fe 80 82 95

[0060] It was experimentally determined that the consumption of biomass of the microorganisms having chemo-organotropic type of exchange in connection with the leaching process was not less than 3×10⁻³ kg per 1 kg of minerals. The degree of extraction of metal decreases if the consumption of biomass is less than 3×10⁻³ kg per 1 kg of minerals for the reason that the quantity of the evolved metabolism products is not sufficient to ensure the transition of these products into solution.

[0061] The method of metal extraction of the present invention thus makes possible an increase in the degree of extraction of metals and a reduction in the duration of the leaching process.

[0062] The specification incorporates by reference the disclosure of Russian priority document 2000-120 926 filed Aug. 10, 2000.

[0063] The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims. 

What is claimed is:
 1. A method for extracting metals from minerals comprising: leaching of metals from a mineral composition with a leaching agent comprised of a biomass of microorganisms which are grown in a nutrient medium and have a heterotrophic type of metabolism.
 2. A method according to claim 1, wherein the microorganisms with a heterotrophic type of metabolism are selected from natural materials.
 3. A method according to claim 1, wherein the leaching is carried out with the consumption of biomass not less than 3×10⁻³ kg per 1 kg of mineral raw material.
 4. A method according to claim 1, wherein the microorganisms with a heterotrophic type of metabolism are at least one of acetic bacteria, pseudomonades, and sulfuric bacteria.
 5. A method according to claim 1, wherein a water solution of higher carbohydrate polymers is used as a nutrient medium.
 6. A method according to claim 1, wherein a mineral additive is introduced into the nutrient medium.
 7. A method according to claim 6, wherein the mineral additive is a selected one of phosphate of ammonia, ammonium chloride, and a mixture of phosphate of ammonia and ammonium chloride.
 8. A method according to claim 6, wherein the mineral additive is sodium chloride.
 9. A method according to claim 1, wherein vegetative residues, sawdust, cane, sedge, and household wastes are used as higher carbohydrate polymers in the nutrient medium. 